If the circuit board has failed, other than a replacement (if one can still even be found) it is possible to replace the individual components.
Had this issue recently with a vintage Kenwood Chef, where the unit would run but only at one speed. The very first time I used the machine for an extended period, one of the capacitors blew, filling the kitchen with acrid smoke. I had a mate who is familiar with electronics solder on a complete new set of capacitors, resistors and triacs, which he sourced from Maplin, and now it works perfectly again. All you have to do is ensure that the new components match the rating of the old ones, so it's a like for like swap - if unsure, take them into the store, and they will find what you need.
If the job isn't something you can do yourself, and you don't know anyone else with the necessary skills, maybe check in the Yellow Pages for a local TV repair shop. Most will consider it to be just another circuit board, and the fact it comes from a vacuum cleaner rather than a TV shouldn't really matter.
